• 공업화학
• /
• 제23권3호
• /
• pp.313-319
• /
• 2012

본 연구에서는 Polyacrylonitrile (PAN)계 탄소섬유 표면에 구리도금 표면처리가 탄소섬유 강화 복합재료의 기계적 계면 특성에 미치는 영향에 관하여 관찰하였다. 탄소섬유 표면특성은 주사전자현미경, X-선 광전자 분광법, X-선 회절분석기, 접촉각 측정기로 측정하였고, 탄소섬유 강화 복합재료의 기계적 계면 물성은 층간전단강도(interlaminar shear strength, ILSS)와 파괴인성(critical stress intensity factor, $K_{IC}$)측정을 통하여 알아보았다. 실험결과로부터, 기계적 계면물성은 탄소섬유 표면에 COOH group과 도금된 구리함량이 증가됨에 따라 순차적으로 증가되는 것이 확인되었으나, 도금시간을 길게 하여 과량의 구리가 도입되었을 경우 기계적 계면 물성을 도리어 감소시키는 것으로 확인되었다. 결론적으로 구리함량이 탄소섬유 복합재료의 기계적 계면물성을 결정하는 중요 요소라 판단되나, 최적의 함량이상에서는 계면분리에 의한 물성저하의 원인이 될 수 있다.

• 콘크리트학회논문집
• /
• 제15권6호
• /
• pp.769-777
• /
• 2003

최근 철근콘크리트(RC) 구조물의 보강기법으로 큰 인장강도와 탄성계수를 갖는 탄소섬유계열 보강재를 사용한 보강공법 개발과 이와 관련된 많은 실험 및 이론적 연구가 진행되고 있다. CFS 및 강판 보강재에 의한 보강시 야기되는 문제점을 해결하기 위하여 대체 재료로 국내에 도입된 탄소섬유메쉬(CFM)를 실 구조물의 보강공사에 적용하기 위하여 우선적으로 CFM을 이용한 보강기법 및 보강된 부재의 구조성능 규명에 대한 연구가 요구되고 있다. 본 연구에서는 탄소섬유메쉬와 콘크리트의 부착특성 규명을 위한 실험적 연구를 수행하였다. 일반적으로 탄소섬유 부착 보강공법은 보강재와 기존 부재와의 부착성능에 의해 보강효과가 지배받게 된다. 즉 부착강도가 충분한 보강효과를 기대할 수 없을 경우의 부착파괴의 가장 큰 원인으로는 계면에서의 전단강도에 기인한다고 할 수 있다. 따라서 본 연구에서는 CFM을 콘크리트에 부착하는데 있어서 정착철물(Clip)의 설치 유무, 정착철물의 정착위치, 정착철물의 설치 열 수, 부착 모르타르의 바름 유무, 부착 모르타르의 바름 두께 등의 실험 변수를 설정하고 인장전단 실험을 수행하였다. 실험결과 적절한 정착철물의 부착위치 및 정착철물 및 부착 모르타르의 부착특성을 규명할 수 있었다. 또한 본 연구에서는 범용 비선형 유한요소 해석 프로그램인 ABAQUS를 이용하여 CFM의 부착특성을 규명하기 위한 유한요소 모델 및 해석기법을 개발하였고 이를 실험결과와 비교하여 이에 대한 검증을 하였다.

• Steel and Composite Structures
• /
• 제21권2호
• /
• pp.343-356
• /
• 2016

As the common cast-in-place construction works fails to meet the enormous construction demand under rapid economic growth, the development of prefabricated structure instead becomes increasingly promising in China. For the prefabricated structure, its load carrying connection joint play a key role in maintaining the structural integrity. Therefore, a novel end plate bolt connecting joint between fully prefabricated pre-stressed concrete beam and high-strength reinforcement-confined concrete column was proposed. Under action of low cycle repeated horizontal loadings, comparative tests are conducted on 6 prefabricated pre-stressed intermediate joint specimens and 1 cast-in-place joint specimen to obtain the specimen failure modes, hysteresis curves, skeleton curves, ductility factor, stiffness degradation and energy dissipation capacity and other seismic indicators, and the seismic characteristics of the new-type prefabricated beam-column connecting joint are determined. The test results show that all the specimens for end plate bolt connecting joint between fully prefabricated pre-stressed concrete beam and high-strength reinforcement-confined concrete column have realized the design objectives of strong column weak beam. The hysteretic curves for specimens are good, indicating desirable ductility and energy dissipation capacity and seismic performances, and the research results provide theoretical basis and technical support for the promotion and application of prefabricated assembly frames in the earthquake zone.

• Advances in concrete construction
• /
• 제9권3호
• /
• pp.313-326
• /
• 2020

Glass fiber-reinforced polymer (GFRP) bars have been introduced as an effective alternative for the conventional steel reinforcement in concrete structures to mitigate the costly consequences of steel corrosion. However, despite the superior performance of these composite materials in terms of corrosion, the effect of replacing steel reinforcement with GFRP on the seismic performance of concrete structures is not fully covered yet. To address some of the key parameters in the seismic behavior of GFRP-reinforced concrete (RC) structures, two full-scale beam-column joints reinforced with GFRP bars and stirrups were constructed and tested under two phases of loading, each simulating a severe ground motion. The objective was to investigate the effect of damage due to earthquakes on the service and ultimate behavior of GFRP-RC moment-resisting frames. The main parameters under investigation were geometrical configuration (interior or exterior beam-column joint) and joint shear stress. The performance of the specimens was measured in terms of lateral load-drift response, energy dissipation, mode of failure and stress distribution. Moreover, the effect of concrete damage due to earthquake loading on the performance of beam-column joints under service loading was investigated and a modified damage index was proposed to quantify the magnitude of damage in GFRP-RC beam-column joints under dynamic loading. Test results indicated that the geometrical configuration significantly affects the level of concrete damage and energy dissipation. Moreover, the level of residual damage in GFRP-RC beam-column joints after undergoing lateral displacements was related to reinforcement ratio of the main beams.

• Geomechanics and Engineering
• /
• 제14권3호
• /
• pp.271-281
• /
• 2018

A jointed rock slope stability evaluation was simulated by a discontinuous deformation analysis numerical method to investigate the process and safety factors for different crack distributions and different overloading situations. An optimized method using Discontinuous Deformation Analysis for Rock Failure (DDARF) is presented to perform numerical investigations on the jointed rock slope stability evaluation of the Dagangshan hydropower station. During the pre-processing of establishing the numerical model, an integrated software system including AutoCAD, Screen Capture, and Excel is adopted to facilitate the implementation of the numerical model with random joint network. These optimizations during the pre-processing stage of DDARF can remarkably improve the simulation efficiency, making it possible for complex model calculation. In the numerical investigations on the jointed rock slope stability evaluations using the optimized DDARF, three calculation schemes have been taken into account in the numerical model: (I) no joint; (II) two sets of regular parallel joints; and (III) multiple sets of random joints. This model is capable of replicating the entire processes including crack initiation, propagation, formation of shear zones, and local failures, and thus is able to provide constructive suggestions to supporting schemes for the slope. Meanwhile, the overloading numerical simulations under the same three schemes have also been performed. Overloading safety factors of the three schemes are 5.68, 2.42 and 1.39, respectively, which are obtained by analyzing the displacement evolutions of key monitoring points during overloading.

• Structural Engineering and Mechanics
• /
• 제55권6호
• /
• pp.1139-1155
• /
• 2015

In this study, a new retrofitting method for improving the seismic performance of reinforced concrete column was presented, in which prestressed steel strips were utilized as retrofitting stuff to confine the reinforced concrete column transversely. In order to figure out the seismic performance of concrete column specimen retrofitted by such prestressed steel strips methods, a series of quasi-static tests of five retrofitted specimens and two unconfined column specimen which acted as control specimens were conducted. Based on the test results, the seismic performance including the failure modes, hysteresis performance, ductility performance, energy dissipation and stiffness degradation of all these specimens were fully investigated and analyzed. And furthermore the influences of some key parameters such as the axial force ratios, shear span ratios and steel strips spacing on seismic performance of those retrofitted reinforced concrete column specimens were also studied. It was shown that the prestressed steel strips provided large transverse confining effect on reinforced concrete column specimens, which resulted in improving the shearing bearing capacity, ductility performance, deformation capacity and energy dissipation performance of retrofitted specimens effectively. In comparison to the specimen which was retrofitted by the carbon fiber reinforced plastics (CFRP) strips method, the seismic performance of the specimens retrofitted by the prestressed steel strips was a bit better, and with much less cost both in material and labor. From this research results, it can be concluded that this new retrofitting method is really useful and has significant advantages both in saving money and time over some other retrofitting methods.

• Computers and Concrete
• /
• 제23권1호
• /
• pp.61-68
• /
• 2019

This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.

• Steel and Composite Structures
• /
• 제51권5호
• /
• pp.509-527
• /
• 2024

Bonding carbon fiber-reinforced polymer (CFRP) laminates have been extensively employed in the restoration of steel constructions. In addition to the mechanical properties of the CFRP, the bond strength (P_U) between the CFRP and steel is often important in the eventual strengthened performance. Nonetheless, the bond behavior of the CFRP-steel (CS) interface is exceedingly complicated, with multiple failure causes, giving the P_U challenging to forecast, and the CFRP-enhanced steel structure is unsteady. In just this case, appropriate methods were established by hybridized Random Forests (RF) and support vector regression (SVR) approaches on assembled CS single-shear experiment data to foresee the P_U of CS, in which a recently established optimization algorithm named Aquila optimizer (AO) was used to tune the RF and SVR hyperparameters. In summary, the practical novelty of the article lies in its development of a reliable and efficient method for predicting bond strength at the CS interface, which has significant implications for structural rehabilitation, design optimization, risk mitigation, cost savings, and decision support in engineering practice. Moreover, the Fourier Amplitude Sensitivity Test was performed to depict each parameter's impact on the target. The order of parameter importance was t_c> L_c > E_A > t_A > E_c > b_c > f_c > f_A from largest to smallest by 0.9345 > 0.8562 > 0.79354 > 0.7289 > 0.6531 > 0.5718 > 0.4307 > 0.3657. In three training, testing, and all data phases, the superiority of AO - RF with respect to AO - SVR and MARS was obvious. In the training stage, the values of R² and VAF were slightly similar with a tiny superiority of AO - RF compared to AO - SVR with R² equal to 0.9977 and VAF equal to 99.772, but large differences with results of MARS.

• 터널과지하공간
• /
• 제32권6호
• /
• pp.568-585
• /
• 2022

본 연구에서는 3차원 입자기반 개별요소모델(grain-based distinct element model, GBDEM)을 이용하여 암석 균열의 열에 의한 미끄러짐 거동을 해석하였다. 이는 DECOVALEX-2023 프로젝트 Task G에 참여하여 수행한 연구로, 해석대상은 한국건설기술연구원에서 수행된 saw-cut 균열 시료에 대한 열-역학적 하중 재하 실험 결과이다. 여기에서는 암석 시험편을 Voronoi 다면체의 집합체로 모델링하고, 개별요소법 코드인 3DEC을 통해 입자와 입자 간 경계면, 내부에 포함된 균열에서의 열-역학적 연계거동을 해석하였다. 주요 해석내용은 가열로 인한 암석 표면의 온도 분포, 열응력의 증가에 따른 주응력 변화, 균열의 전단변위와 수직변위이다. 해석 결과, 상기 수치모델은 실내실험에서 관찰된 열전달과 열손실 특성, 열에 의한 균열의 점진적 전단파괴 프로세스, 변위의 제한으로 인한 열응력의 증가 등을 합리적 수준에서 재현하고 있는 것으로 나타났다. 그러나 가열에 의한 전단파괴 시점, 열응력 증분과 변위 크기 등에서는 다소 차이를 보였다. 본 연구의 해석모델은 Task G에 참여하는 국외 연구팀들과의 의견 교류 및 협력을 통해 지속적으로 개선, 검증할 예정이다.

• 한국건설순환자원학회논문집
• /
• 제5권3호
• /
• pp.290-297
• /
• 2017

압축강도 160MPa와 길이 15.4m를 가진 분절형 U거더와 합성 U거더의 휨거동 실험을 수행하였다. 실험 변수로는 강섬유 혼입률과 U거더 상부의 슬래브이다. U거더의 복부와 하부플랜지에 종방향 철근을 배근하였다. 상부플랜지에 2개의 15.2mm 강연선을 포함한 2개의 프리스트레싱 텐던 그리고 하부플랜지에 7개의 15.2mm 강연선을 포함한 2개의 프리스트레싱 텐던이 배치되고 U거더 접합 시 한차례 긴장 작업을 하였다. 초고강도 콘크리트 강도로 인해 U거더에 도입한 충분히 강한 프리스트레싱 긴장력은 U거더 시공단계에서 자중과 고정하중을 부담할 수 있다. U거더의 취성적 거동에 비해 합성 U거더는 안정적이고 연성적인 하중처짐 관계를 보여주고 있다. U거더 상부에 슬래브를 시공한 후, U거더 접합 시 도입했던 프리스트레싱 긴장력에 의한 합성 U거더의 휨하중 내하력은 마지막 하중 단계에서 설계하중을 부담할 수 있다. 초고강도 콘크리트로 인한 간단한 프리스트레싱 방법은 시공단계와 공사비 면에서 장점을 가지고 있다. 간격이 작은 전단키는 초고강도 콘크리트 U거더와 고강도 콘크리트슬래브간의 완전한 합성관계를 가져와 파괴하중 직전까지 슬립현상이나, 벌어짐 현상을 보이지 않았다.